1. Field of the Invention
The present invention relates to a method of leaching a metal value from a heap of a metal-containing ore.
The present invention relates particularly to distributing leach liquors onto top surfaces of heaps in order to optimise leaching of the heaps.
U.S. Pat. No. 6,216,962 in the name of Krieg describes heap leaching in the following terms.
2. Description of the Prior Art
“In the commercial practice of hydrometallurgy, a bed of run-of-mine or granular low grade ore, known as a heap, is spread over an impervious base or pad which may comprise sheets of plastic film, asphalt and/or compacted clay. Crushed ore is normally heaped onto the pad to a depth to 10 to 30 feet and leveled off at the top of the heap. The ore is typically pre-crushed to a desired size.”
“After the heap has been prepared, the target metal is leached from the ore by circulating the leaching solution through the heap in a process commonly known as percolation. To effect percolation, the solution is distributed over the top of the heap and permitted to seep down through the heap to the impervious pad. The impervious pad is typically sloped toward a drain pipe or channel for recovering the metal laden solution. The liquid that is distributed over the top of the heap may be a leaching solution comprising water mixed with a leaching agent, or a leaching agent may be premixed with the ore before the ore is spread onto the heap and relatively pure water is percolated through the heap.”
The term “leach liquor” is herein understood to mean the liquid that is distributed over the top of a heap in a heap leaching method. As indicated in the above-quoted passages from the Kreig US patent, the liquid may be (a) a leaching solution that includes a leaching agent and water or (b) water—in situations where a leaching agent has been pre-mixed with ore in a heap.
There are a number of known options for distributing a leach liquor onto a top surface of a heap.
The options are generally based on the use of sprayer/sprinkler systems or drip systems positioned at various locations on top surfaces of heaps.
In some instances, the known options are relatively complicated. For example, U.S. Pat. No. 5,005,806 in the name of Krauth discloses a drip system that includes mainline pipes extending longitudinally along a side of a heap, parallel header pipes extending at spaced intervals from the main pipeline across the heap, and parallel, closely spaced tubes extending longitudinally between the header pipes, each tube having a plurality of outlets for leach liquor.